1. Field of the Invention
This invention broadly relates to a bone screw useful for fastening external splints, as applied to a fractured limb by orthopedic surgery in order to stabilize the bone fracture.
In particular, the invention relates to a bone screw having an elongate cylinder body of predetermined length, a threaded end portion terminating with a tip, and an opposite screw-handling end.
2. Prior Art
As it is well known in this specific technical field, one of the most effective methods for stabilizing bone fractures is based on the use of external splints, whereby fractures at particularly delicate locations, e.g. close to the joints, or fractures with attendant serious injury of the cutaneous tissue, can be set in all those cases in which the traditional plaster could be unsuitable or even impracticable.
Such splints are fastened at their opposite ends to respective undamaged portions of the broken bone, specifically to opposite sides of the fracture. The splint ends are fastened by means of bone screws which are firmly implanted in the bone itself.
In the instance of a tibial fracture, for example, the opposite ends of a respective tibial external splint are fastened on either sides of the fracture using appropriate bone screws. In other instances, when the fracture affects a joint, such as an ankle, the bone screws of a respective ankle external splint are implanted into the tibia and the talus.
These bone screws are to provide reliable anchor points for the external splint device. To this aim, they generally comprise:
a screw shank, having a substantially elongate cylindrical shape;
a threaded screw portion, generally tapering toward a tip;
an opposite screw-handling end, that is a screw head structure and adapted for engagement by a driving tool, such as a wrench or a power driver.
Advantageously, the screw head consists of a short flat lying portion, which is parallel to the screw axis and formed by a milling process at the screw end opposite to the tip.
In view of the bulky size of the above external splint apparatus and of its sticking out in the installed position from one side of the fractured limb, it will be appreciated that a splint device may constitute a bulky interfering attachment for both the operating personnel and the patient. Accordingly, in this field it exists the need of reducing or at least of limiting such encumbrance.
A way of filling this demand is, for example, that of using bone screws of different length and such that the ultimate implanted screws will jut a shorter length out of the splint device.
For the purpose, the prior art provides each splint with a plentiful range of bone screws, all alike in shape and construction but having different lengths. Thus, the orthopedic surgeon will always have the screw with the most appropriate length available for each case, and in the implanted state, the screw will not jut out of the splint device, although its handling end can still be easily reached.
This is a widely accepted and fairly satisfactory solution, but it can not fill the demands of every surgical situation. Besides, it still exhibits technical shortcomings such asxe2x80x94perhaps most importantlyxe2x80x94the difficulty represented by the need to select the bone screw with the most suitable length xe2x80x9con the spotxe2x80x9d, since once the screw implanting operation is in progress using the selected screw, it is inconvenient or impossible to interrupt such operation to substitute said screw with a more suitable one. Because of the difficulty experienced in selecting the screw with the most suitable length xe2x80x9con the spotxe2x80x9d, it is not infrequent for one or more bone screws to jut out undesirably of the external splint after installation, resulting in the aforementioned drawbacks.
Another shortcoming is the large number of screws that must be made available in order to cover the largest possible number of operative situations, which can occur. On the one side, this makes the selection less obvious, and on the other, weighs heavily on the overall cost for equipment.
FR 2 751 523 discloses a self tapping screw for fixing osteosynthesis plate. The screw comprises a self-tapping threaded shank with a head connected by an intermediate brittle area to a gripping end to be inserted into the barrel of a screw driving tool.
U.S. Pat. No. 5,487,744 discloses a spinal fixation device for immobilizing a portion of a spine which includes at least one spine rod and a plurality of bone screws that are threaded into an appropriate number of vertebrae and each of which includes a threaded end protruding from the vertebra. Clamps are used to fasten a spine rod to the bone screws.
EP 0729731 discloses a fixation system of column constituted by a fitting of vertebral column, a pedicular stem which can be used in the case of a traction as well as in the case of a fracture, a bolt screw provided with a cylindrical recess, a nut and a cylinder shaped bar with flat exterior surface.
U.S. Pat. No. 4,778,388 discloses a root canal post for use in constructing a therapeutic foundation on the root tooth for treatment of a broken tooth, the post comprising a head, a shank and a bore axially produced through the head and shank. The bore includes a filler releasably filled therein so that after the post is anchored in the tooth, a subsequent treatment for a possible secondary cavities is applied through the bore which is made empty by removing the filler.
However, the heads of the screw according to FR 2 751 523 and the post according to U.S. Pat. No. 4,778,388 have a diameter higher than that of their respective shanks, the bolt screw according to EP 0 729 731 is to be allocated into a cylindrical hollow space of the fixation system and the screw according to U.S. Pat. No. 5,487,744 is provided with two opposite threaded ends for anchoring the screw in a vertebra and for fastening the screw to the clamp respectively.
Due to the above characteristics, all the screws according to FR 2 751 523, U.S. Pat. No. 4,778,388, EP 0 729 731 and U.S. Pat. No. 5,487,744 have a fixed length and therefore display the same inconveniences as those of the above-cited prior art screws.
U.S. Pat. No. 6,004,327 discloses a ratcheting compression device which can be customized in length and comprises two pieces, of which one is a pin comprising an elongate cylindrical body of predetermined length having located at or near its distal end a threaded portion and having preferably a substantially smooth portion at or near its proximal end.
However, although the threaded portion of the pin terminates with a tip, a substantial part of the above threaded portion has an outside diameter which is higher than the diameter of the cylindrical body.
Furthermore, the pin is provided near its mid portion with ratcheting means, preferably asymmetric teeth, which cooperate with anti-rotation means provided on the other piece of the device according to U.S. Pat. No. 6,004,327 in order to compress two segments of bone together.
The underlying technical problem of this invention is to contrive a bone screw with structural and functional features able to overcome the aforementioned disadvantages. The invention devises a xe2x80x9cuniversalxe2x80x9d bone screw, which allows a substantially univocal selection of such screw in all types of external splint installations, and drastically cuts down the expenses due to the necessity of requiring a comprehensive set of screws which are similar in structure, but have different lengths.
The principle of this invention is to have a handling end of the screw of substantially the same diameter as that of the screw body and formed with flats alternating with lands which extend over the main part of the screw body.
Based on this principle, the technical problem is solved by a bone screw as previously indicated and characterized in the following claims.
The features and advantages of a bone screw according to the invention will be apparent in the following description of an embodiment thereof, to be read with reference to the accompanying non-limitative drawings.